Hydrocarbon manufacture from alcohols

ABSTRACT

A catalytic process is provided for converting a feed containing a C 1  -C 4  monohydric alcohol by contact of said alcohol, under conversion conditions, with a catalyst comprising a crystalline aluminosilicate zeolite having a crystal size of at least about 1 micron, a silica to alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12. The zeolite contains a Group 2B and a Group 8 metal or metal compound plus magnesium, either per se or in compound form.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.20,160, filed Mar. 14, 1979, now abandoned, which in turn is adivisional of U.S. application Ser. No. 896,267, filed Apr. 14, 1978 nowU.S. Pat. No. 4,148,835.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a specified crystalline aluminosilicatezeolite catalyst characterized by a crystal size of at least about 1micron. It has associated with it a Group 2B metal, a Group 8 metal andmagnesium. The invention also relates to a method of making thecatalyst.

2. Description of the Prior Art

A remarkable growth in the production of synthetic fibers, plastics andrubber has taken place in recent decades. This growth, to a very largeextent, has been supported and encouraged by an expanding supply ofinexpensive petrochemical raw materials such as ethylene, benzene,toluene and xylenes.

Increasing demand for olefins, e.g. C₂ -C₃ olefins has, from time totime, led to periods of shortage, either due to a diminished supply ofsuitable feedstocks or to limited processing capacity. In any event, itis desirable to provide efficient means for converting raw materialsother than petroleum to olefins.

Understandably, there has been considerable effort made to find new waysto produce certain olefin hydrocarbons. For example, U.S. Pat. No.4,025,571 discloses the conversion of a feed of alcohols, ethers andmixtures thereof to hydrocarbons rich in C₂ - and C₃ hydrocarbons andcertain aromatics by passing the feed over the specified zeolites.

SUMMARY OF THE INVENTION

In accordance with the present invention, there has been discovered acatalyst comprising a crystalline aluminosilicate zeolite having acrystal size of at least about 1 micron, usually in the approximaterange of 1-20 microns and preferably 1-6 microns. The crystallinealuminosilicate zeolite is essentially characterized by a silica toalumina ratio of at least about 12, a constraint index within theapproximate range of 1 to 12 and the presence therein of a Group 2B anda Group 8 metal or metal compound and magnesium or its oxide or sulfide,these being incorporated into the catalyst in the order mentioned. Theinvention also provides a method for making the catalyst.

DESCRIPTION OF SPECIFIC EMBODIMENTS

It is contemplated that feed comprising any monohydric alcohol havingfrom 1 to 4 carbon atoms may be used as feed to the process of thisinvention. Thus, methanol, ethanol, n-propanol, isopropanol, n-butanol,sec-butanol and isobutanol may be used either alone or in admixture withone another. The particularly preferred feed is methanol.

In accordance with the present invention, such feed is brought intocontact, under conversion conditions, with a catalyst comprising acrystalline aluminosilicate zeolite having a crystal size of at leastabout 1 micron, a silica to alumina ratio of at least about 12 and aconstraint index within the approximate range of 1 to 12, and havingzinc, palladium and magnesium oxide associated therewith.

The zeolites herein described are members of a class of zeolitesexhibiting some unusual properties. These zeolites induce profoundtransformations of aliphatic hydrocarbons to aromatic hydrocarbons incommercially desirable yields and are generally highly effective inconversion reactions involving aromatic hydrocarbons. Although they haveunusually low alumina contents, i.e. high silica to alumina ratios, theyare very active even when the silica to alumina ratio exceeds 30. Theactivity is surprising since catalytic activity is generally attributedto framework aluminum atoms and cations associated with these aluminumatoms. These zeolites retain their crystallinity for long periods inspite of the presence of steam at high temperature which inducesirreversible collapse of the framework of other zeolites, e.g. of the Xand A type. Furthermore, carbonaceous deposits, when formed, may beremoved by burning at higher than usual temperatures to restoreactivity. In many environments the zeolites of this class exhibit verylow coke forming capability, conducive to very long times on streambetween burning regenerations.

An important characteristic of the crystal structure of this class ofzeolites is that it provides constrained access to, and egress from theintracrystalline free space by virtue of having a pore dimension greaterthan about 5 Angstroms and pore windows of about a size such as would beprovided by 10-membered rings of oxygen atoms. It is to be understood,of course, that these rings are those formed by the regular dispositionof the tetrahedra making up the anionic framework of the crystallinealuminosilicate, the oxygen atoms themselves being bonded to the siliconor aluminum atoms at the centers of the tetrahedra. Briefly, thepreferred type zeolites useful in this invention possess, incombination: a silica to alumina ratio of at least about 12; and astructure providing a constrained access to the crystalline free space.

The silica to alumina ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminaratio of at least 12are useful, it is preferred to use zeolites havinghigher ratios of at least about 30. Such zeolite, after activation,acquire an intracrystalline sorption capability for normal hexane whichis greater than that for water, i.e. they exhibit "hydrophobic"properties. It is believed that this hydrophobic character isadvantageous in the present invention.

The type zeolites useful in this invention freely sorb normal hexane andhave a pore dimension greater than about 5 Angstroms. In addition, thestructure must provide constrained access to larger molecules. It issometimes possible to judge from a known crystal structure whether suchconstrained access exists. For example, if the only pore windows in acrystal are formed by 8-membered rings of oxygen atoms, then access bymolecules of larger cross-section than normal hexane is excluded and thezeolite is not of the desired type. Windows of 10-membered rings arepreferred, although, in some instances, excessive puckering or poreblockage may render these catalysts ineffective. Twelve-membered ringsdo not generally appear to offer sufficient constraint to produce theadvantageous conversion, although puckered structures exist such as TMAoffretite which is a known effective zeolite. Also, structures can beconceived, due to pore blockage or other cause, that may be operative.

Rather than attempt to judge from crystal structure whether or not acatalyst possesses the necessary constrained access, a simpledetermination of the "constraint index" may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a small sample, approximately 1 gram or less, ofzeolite at atmospheric pressure according to the following procedure. Asample of the zeolite, in the form of pellets or extrudate, is crushedto a particle size about that of coarse sand and mounted in a glasstube. Prior to testing, the zeolite is treated with a stream of air at1000° F. for at least 15 minutes. The zeolite is then flushed withhelium and the temperature adjusted between 550° F. and 950° F. to givean overall conversion between 10% and 60%. The mixture of hydrocarbonsis passed at 1 liquid hourly space velocity (i.e., 1 volume of liquidhydrocarbon per volume of zeolite per hour) over the zeolite with ahelium dilution to give a helium to total hydrocarbon mole ratio of 4:1.After 20 minutes on stream, a sample of the effluent is taken andanalyzed, most conveniently by gas chromatography, to determine thefraction remaining unchanged for each of the two hydrocarbons.

The "constraint index" is calculated as follows: ##EQU1##

The constraint index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Catalysts suitable for the presentinvention are those having a constraint index in the approximate rangeof 1 to 12. Constraint index (CI) values for some typical catalysts are:

    ______________________________________                                        CAS                 C.I.                                                      ______________________________________                                        ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-12              2                                                         ZSM-38              2                                                         ZSM-35              4.5                                                       TMA Offretite       3.7                                                       Beta                0.6                                                       ZSM-4               0.5                                                       H-Zeolon            0.5                                                       REY                 0.4                                                       Amorphous Silica-Alumina                                                                          0.6                                                       Erionite            38                                                        ______________________________________                                    

It is to be realized that the above constraint index values typicallycharacterize the specified zeolites but that such are the cumulativeresult of several variables used in determination and calculationthereof. Thus, for a given zeolite depending on the temperature employedwithin the aforenoted range of 550° F. to 950° F. with accompanyingconversion between 10% and 60%, the constraint index may vary within theindicated approximate range of 1 to 12. Likewise, other variables suchas the crystal size of the zeolite, the presence of possibly occludedcontaminants and binders intimately combined with the zeolite may affectthe constraint index. It will accordingly be understood by those skilledin the art that the constraint index, as utilized herein, whileaffording a highly useful means for characterizing the zeolites ofinterest is approximate, taking into consideration the manner of itsdetermination, with the probability, in some instances, of compoundingvariable extremes. However, in all instances, at a temperature withinthe above-specified range of 550° F. to 950° F., the constraint indexwill have a value for any given zeolite of interest herein within theapproximate range of 1 to 12.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-11,ZSM-12, ZSM-35,

ZSM-38 and other similar materials. U.S. Pat. No. 3,702,886 describingand claiming ZSM-5 is incorporated herein by reference.

ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which are incorporated herein by reference.

ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, theentire contents of which are incorporated herein by reference. ZSM-38 ismore particularly described in U.S. Pat. No. 4,046,859.

The synthetic ZSM-35 zeolite possesses a definite distinguishingcrystalline structure whose x-ray diffraction pattern showssubstantially the significant lines set forth in Table II. It isobserved that this x-ray diffraction pattern (with respect tosignificant lines) is similar to that of natural ferrierite with anotable exception being that natural ferrierite patterns exhibit asignificant line at 11.33A. Close examination of some individual samplesof ZSM-35 show a very weak line at 11.3-11.5A. This very weak line,however, is determined not to be a significant line for ZSM-35.

                  TABLE II                                                        ______________________________________                                        d(A)          I/Io                                                            ______________________________________                                         9.6 ± 0.20                                                                              Very Strong-Very Very Strong                                    7.10 ± 0.15                                                                              Medium                                                          6.98 ± 0.14                                                                              Medium                                                          6.64 ± 0.14                                                                              Medium                                                          5.78 ± 0.12                                                                              Weak                                                            5.68 ± 0.12                                                                              Weak                                                            4.97 ± 0.10                                                                              Weak                                                            4.58 ± 0.09                                                                              Weak                                                            3.99 ± 0.08                                                                              Strong                                                          3.94 ± 0.08                                                                              Medium Strong                                                   3.85 ± 0.08                                                                              Medium                                                          3.78 ± 0.08                                                                              Strong                                                          3.74 ± 0.08                                                                              Weak                                                            3.66 ± 0.07                                                                              Medium                                                          3.54 ± 0.07                                                                              Very Strong                                                     3.48 ± 0.07                                                                              Very Strong                                                     3.39 ± 0.07                                                                              Weak                                                            3.32 ± 0.07                                                                              Weak Medium                                                     3.14 ± 0.06                                                                              Weak Medium                                                     2.90 ± 0.06                                                                              Weak                                                            2.85 ± 0.06                                                                              Weak                                                            2.71 ± 0.05                                                                              Weak                                                            2.65 ± 0.05                                                                              Weak                                                            2.62 ± 0.05                                                                              Weak                                                            2.58 ± 0.05                                                                              Weak                                                            2.54 ± 0.05                                                                              Weak                                                            2.48 ± 0.05                                                                              Weak                                                            ______________________________________                                    

A further characteristic of ZSM-35 is its sorptive capacity proving saidzeolite to have increased capacity for 2-methylpentane (with respect ton-hexane sorption by the ratio n-hexane/2-methylpentane) when comparedwith a hydrogen form of natural ferrierite resulting from calcination ofan ammonium exchanged form. The characteristic sorption ration-hexane/2-methylpentane for ZSM-35 (after calcination of 600° C.) isless than 10, whereas that ratio for the natural ferrierite issubstantially greater than 10, for example, as high as 34 or higher.

Zeolite ZSM-35 can be suitably prepared by preparing a solutioncontaining sources of an alkali metal oxide, preferably sodium oxide, anorganic nitrogen-containing oxide, an oxide of aluminum, an oxide ofsilicon in water and having a composition, in terms of mole ratios ofoxides, falling within the following ranges:

    ______________________________________                                        R+             Broad        Preferred                                         ______________________________________                                        R+ + M+        0.2-1.0      0.3-0.9                                           OH.sup.- /SiO.sub.2                                                                          0.05-0.5     0.07-0.49                                         H.sub.2 O/OH.sup.-                                                                           41-500       100-250                                           SiO.sub.2 /Al.sub.2 O.sub.3                                                                  8.8-200      12-60                                             ______________________________________                                    

wherein R is an organic nitrogen-containing cation derived frompyrrolidine or ethylenediamine and M is an alkali metal ion, andmaintaining the mixture until crystals of the zeolite are formed. (Thequantity of OH⁻ is calculated only from the inorganic sources of alkaliwithout any organic base contribution.) Thereafter, the crystals areseparated from the liquid and recovered. Typical reaction conditionsconsist of heating the foregoing reaction mixture to a temperature offrom about 90° C. to about 400° C. for a period of time of from about 6hours to about 100 days. A more preferred temperature range is fromabout 150° C. to about 400° C. with the amount of time at a temperaturein such range being from about 6 hours to about 80 days.

The digestion of the gel particles is carried out until crystals form.The solid product is separated from the reaction medium, as by coolingthe whole to room temperature, filtering and water washing. Thecrystalline product is dried, e.g., at 230° F., for from about 8 to 24hours.

The specific zeolites described, when prepared in the presence oforganic cations, or catalytically inactive, possibly because theintracrystalline free space is occupied by organic cations from theforming solution. They may be activated by heating in an inertatmosphere at 1000° F. for 1 hour, for example, followed by baseexchange with ammonium salts followed by calcination at 1000° F. in air.The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this type zeolite; however, thepresence of these cations does appear to favor the formation of thisspecial type of zeolite. More generally, it is desirable to activatethis type catalyst by base exchange with ammonium salts followed bycalcination in air at about 1000° F. for from about 15 minutes to about24 hours.

Natural zeolites may sometimes be converted to this type zeolitecatalyst by various activation procedures and other treatments such asbase exchange, steaming, alumina extraction and calcination, incombinations. Natural minerals which may be so treated includeferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite,clinoptilolite. The preferred crystalline aluminosilicates are ZSM-5,ZSM-11, ZSM-12, ZSM-38, and ZSM-35, with ZSM-5 particularly preferred.

The catalyst of this invention may be in the hydrogen form, but theywill contain a Group 2B metal, such as zinc, a Group 8 metal, such aspalladium and magnesium. It will be understood that "metal" includesalso its compound form, especially the oxide or the sulfide. It isdesirable to calcine the catalyst after base exchange.

In a preferred aspect of this invention, the catalysts hereof areselected as those having a crystal framework density in the dry hydrogenform, of not substantially below about 1.6 grams per cubic centimeter.Therefore, the preferred catalysts of this invention are those having aconstraint index as defined above of about 1 to about 12, asilica-to-alumina of at least about 12 and a dried crystal density ofnot less than about 1.6 grams per cubic centimeter. The dried densityfor known structures may be calculated from the number of silicon plusaluminum atoms per 1000 cubic Angstroms, as given, e.g., on page 19 ofthe article on zeolite structure by W. M. Meier. This paper, the entirecontents of which are incorporated herein by reference, is included in"Proceedings of the Conference on Molecular Sieves, London, April,1967," published by the Society of Chemical Industry, London, 1968. Whenthe crystal structure is unknown, the crystal framework density may bedetermined by classical pyknometer techniques. For example, it may bedetermined by immersing the dried hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. It is possible thatthe unusual sustained activity and stability of this class of zeolite isassociated with its high crystal anionic framework density of not lessthan about 1.6 grams per cubic centimeter. This high density, of course,must be associated with a relatively small amount of free space withinthe crystal, which might be expected to result in more stablestructures. This free space, however, is important as the locus ofcatalytic activity.

Crystal framework densities of some typical zeolites are:

    ______________________________________                                                        Void             Framework                                    Zeolite         Volume           Density                                      ______________________________________                                        Ferrierite      0.28   cc/cc     1.76 g/cc                                    Mordenite       .28              1.7                                          ZSM-5, -11      .29              1.79                                         Dachiardite     .32              1.72                                         L               .32              1.61                                         Clinoptilolite  .34              1.71                                         Laumontite      .34              1.77                                         ZSM-4  Omega)   38               1.65                                         Heulandite      .39              1.69                                         P               .41              1.57                                         Offretite       .40              1.55                                         Levynite        .40              1.54                                         Erionite        .35              1.51                                         Gmelinite       .44              1.46                                         Chabazite       .47              1.45                                         A               .5               1.3                                          Y               .48              1.27                                         ______________________________________                                    

The crystal size of the synthesized zeolite has been found to be animportant factor affecting the desired conversion of the describedalcohol and/or ether charge stock to low molecular weight olefins andparaxylene. The crystal size of the above-described crystallinealuminosilicate zeolite employed in the process of the invention is atleast about 1 micron, being in the approximate range of 1-20 microns andparticularly in the range of 1-6 microns. With the use of crystalswithin such size range, distinctly higher selectivity for production ofthe desired C₂ -C₃ olefins and paraxylene has been observed as comparedwith comparable use of smaller size crystals.

When synthesized in the alkali metal form, the zeolite is convenientlyconverted to the hydrogen form, generally by intermediate formation ofthe ammonium form as a result of ammonium ion exchange and calcinationof the ammonium form to yield the hydrogen form. In addition to thehydrogen form, other forms of the zeolite wherein the original alkalimetal has been reduced to less than about 0.1 percent by weight may beused.

The preferred catalyst will contain from about 0.1% to about 10%,preferably about 1% to about 5% by weight of the Group 2B component, of,as for example, zinc, about 0.1% to about 5%, preferably about 0.5% toabout 2% by weight of the Group 8 component, for example, palladium andabout 0.1% to about 30%, preferably 5% to about 15% by weight of themagnesium component. These concentrations apply whether they concern themetal per se or its compound form.

It may be desirable in some instances to incorporate the zeolite inanother material resistant to the temperatures and other conditionsemployed in the conversion process. Such matrix materials are to bedistinguished from the aforenoted inert diluents and include syntheticor naturally occurring substances as well as inorganic materials such asclay, alumina or other metal oxides. The latter may be either naturallyoccurring or in the form of gelatinous precipitates or gels includingmixtures of silica and metal oxides. Naturally occurring clays which canbe composited with the zeolite include those of the montmorillonite andkaolin families, which families include the sub-bentonites and thekaolins commonly known as Dixie, McNamee-Georgia and Florida clays orothers in which the main mineral constituent is halloysite, kaolinite,dickite, nacrite or anauxite. Such clays can be used in the raw statesas originally mined or initially subjected to calcination, acidtreatment or chemical modification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-berylia, silica-titania as well as ternary compositions, such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia. The matrix may be in the form of a cogel.The relative proportion of finely divided zeolite and inorganic oxidegel matrix may vary widely with the zeolite content ranging from between1 to about 99 percent by weight and more usually in the range of about 5to about 80 percent by weight of the composite. In the process of thisinvention, the feed consisting essentially of one or more of thealcohols is contacted with the above-described catalyst bed at atemperature of about 500° F. to about 950° F. and preferably about 600°F. to about 850° F.; a contact time equivalent to or the same as aweight hourly space velocity (WHSV) of about 1 to about 100 preferablyabout 2 to about 40, it being understood that WHSV signifies pounds offeed per pound of zeolite per hour; and at an absolute pressure of about0.2 to about 50 atmospheres, preferably between about 1 and about 30atmospheres.

The reaction product effluent from the process of the invention containssteam and a hydrocarbon mixture particularly rich in the light olefins,ethylene and propylene with some aromatic hydrocarbons with highselectivity for paraxylene. Generally, a major fraction of the totalolefins, calculated on a mol basis, is ethylene plus propylene. Thepredominant aromatic hydrocarbons are monocyclic hydrocarbons, notablyC₈ and C₉ + aromatics with a high proportion of paraxylene. Thus, thepredominant hydrocarbons are all valuable petrochemicals. The steam andhydrocarbons are separated from one another by methods well known in theart.

Catalyst deactivated by coke deposited during the process may beregenerated by calcining in an oxygen-containing atmosphere, e.g. air,at an elevated temperature within the approximate range of 600° F. to1200° F. for a period of between about 1 and about 30 hours.

The following examples will serve to illustrate the process of thisinvention without limiting the same:

Catalyst Preparation

ZSM-5C was made conventionally using the tetrapropylammonium and sodiumcations. It was calcined and ion exchanged with the ammonium cation toyield the NH₄ ZSM-5C utilized as described hereinafter.

Eleven grams of this NH₄ ZSM-5C was calcined for 2 hours at 1000° F.,300 ml. air flow. Then 2.63 of Zn(NO₃)₂. 6H₂ was added to 16 ml. ofwater and the calcined catalyst was added thereto with stirring. Thematerial was dried at 2 hours at 266° F. and was then calcined for 2hours at 1000° F. in air.

Palladium chloride, 0.095 g., was dissolved in concentrated ammoniumhydroxide and this solution was diluted to 18 ml. with hot water. TheZnZSM-5C was added with stirring. After completion of the impregnation,the ZnPdZSM-5 was dried for 2 hours at 266° F. and then was calcined for2 hours at 1000° F.

To 10 ml. of water was added 1.85 g. of magnesium acetate and thissolution was added to the ZnPdZSM-5C, which was 40/60 mesh. The excesswater was evaporated under a heat lamp and the product was calcined for17 hours at 572° F. and at 896° F. for 4 hours.

The product, ZnPdMgOZSM-5C, contained 0.5% palladium, 4.5% zinc and 10%magnesium oxide.

The conversion reactions were carried out in a vertically-mounted vycormicroreactor, heated by a low heat capacity resistance furnace. Thecatalyst (40-60 mesh) was centered between layers of pyrex chips. Thefeed, 20% wt. % methanol in water was pumped upflow over the catalystbed. The reactor effluent passed through heat traced lines to a heatedsample valve mounted on an HP 5750 gas chromatograph.

It will be understood that the feed may comprise the C₁ -C₄ alkanolalone, or admixed with water or admixed with corresponding ethers, i.e.,those containing a total of 2-8 carbon atoms. The reactor effluent wasanalyzed on a 12 ft. 1/8" column packed with n-octane on Porosil "C".The gas chromatograph program consisted of a five minute initial hold atroom temperature, followed by a programmed heating rate of 15° C./minuteto 160° C. and final hold. Sensitivity factors for hydrocarboncomponents were taken as unity, for dimethylether 3.0 and for methanol3.6. Conversion was calculated on the basis of the CH₂ content ofmethanol feed. The hydrogen, carbon monoxide and carbon dioxide contentof the effluent gas stream was monitored qualitatively by periodicsampling and gas chromatograph analysis with the HP refinery gasanalyzer.

The conversion reactions can be run at from about 400° F. to about 1000°F., preferably about 500° F. to 700° F., at an LHSV of from about 0.1 toabout 10, preferably about 0.5 to 3 and at a pressure of from about 0.5to about 20 atmospheres, preferably about 1 to 5 atmospheres.

A representative listing of the hydrocarbon product distribution for themagnesium oxide modified catalyst is presented in Table 1.

                  TABLE 1                                                         ______________________________________                                        Product Composition                                                           Methanol Conversion Studies                                                   Pd/ Zn/ MgO/ZSM-5C                                                                      Hydrocarbon Composition, wt. %                                      Product     1         2        3      4                                       ______________________________________                                        methane     7.8       0.2      0.3    0.4                                     ethane      1.0       0.2      0.5    0.3                                     ethylene    53.4      45.9     43.5   50.6                                    propane     2.6       2.4      3.7    1.9                                     propylene   16.0      27.4     24.9   25.6                                    C.sub.4 olefins                                                                           2.6       5.1      8.0    5.2                                     C.sub.4 paraffins                                                                         2.6       6.0      3.7    7.9                                     C.sub.5.sup.+                                                                             1.6       0.9      3.6    0.9                                     aromatics   12.4      11.9     11.8   7.2                                     aromatics/C.sub.5.sup.+                                                                   88.6      93.0     76.6   88.9                                    total olefins                                                                             72.0      78.4     76.4   81.4                                    conversion                                                                    (CH.sub.2 basis)                                                                          27.6      41.9     71.1   22.4                                    ______________________________________                                         Run conditions:                                                               Sample 1; 707° F., T.O.S. 26.0 hrs. initial, 1.1 LHSV.                 Sample 2; 564° F., T.O.S. 21.0 hrs. after 2nd. regeneration, 1.4       LHSV.                                                                         Sample 3; 581° F., T.O.S. 21.0 hrs. after 3rd. regeneration, 1.2       LHSV.                                                                         Sample 4; 554° F., T.O.S. 28.0 hrs., after 3rd. regeneration, 1.2      LHSV.                                                                    

With methanol as the feed, it has been found that to get the maximumethylene yield, the zinc, palladium, and magnesium must be added to thezeolite in a specific order as described hereinabove, i.e., by addingzinc, palladium, and magnesium oxide, in that preferred order.Furthermore, it is preferred that the zinc, palladium and magnesium beimpregnated into the zeolite. It may also be added by exchanging thezinc and palladium and by impregnating the magnesium.

Table 2 presents selectivity data obtained during methanol conversionover a ZSM-5 catalyst comprising the ions shown. All ions were made apart of the catalyst by impregnation under conditions similar to thoseof the above-noted catalyst preparation. The conversion reaction wasconducted using 20 wt. % of methanol in water in accordance with theprocedure disclosed above.

                  TABLE 2                                                         ______________________________________                                                                  C.sub.2 = Selecti-                                           Steps            vity at 60%                                         (1)             (2)      (3)      Conversion                                  ______________________________________                                        Unmodified                          29                                        One-Component                                                                 System                                                                        WJR193     15%MgO                                                                        as (OAc) --       --     31                                        Two-Component                                                                 System                                                                        M77-14     4.5%Zn   0.5%Pd   --     35                                        WJR184-B-1 0.5%Pd   10%MgO                                                                        as (OAc) --     33                                        WJR184-C-1 2.5%Zn   10%MgO                                                                        as (OAc) --     32                                        WJR184-C-2 4.5%Zn   10%MgO                                                                        as (OAc) --     35                                        Three-Component                                                               System                                                                        WJR178     4.5%Zn   0.5%Pd   10%MgO                                                                        as (OAc)                                                                             45                                        WJR174     4.5%Zn   0.5%Pd   10%MgO                                                                        as (OAc)                                                                             47                                        WJR195*    4.5%Zn   0.5%Pd   10%MgO                                                                        as (OAc)                                                                             42                                        WJR184-B-3 0.5%Pd   4.5%Zn   10%MgO                                                                        as (OAc)                                                                             36                                        WJR186     0.5%Pd                                                                        4.5%Zn   --       --     37                                                   10%MgO                                                                        as (OAc)                                                           ______________________________________                                         *powder-                                                                 

We claim:
 1. A crystalline aluminosilicate zeolite catalyst having a crystal size of at least about 1 micron, a silica-to-alumina ratio of at least about 12 and a constraint index of about 1 to about 12, said zeolite comprising a Group 2B component, a Group 8 component and magnesium that have been incorporated into said zeolite in that order.
 2. The catalyst of claim 1 wherein the Group 2B metal is zinc and the Group 8 metal is palladium.
 3. The catalyst of claim 2 wherein the magnesium is in the form of magnesium oxide.
 4. The catalyst of claim 2 wherein the zinc and palladium are added by impregnation.
 5. The catalyst of claim 3 wherein the zinc, palladium and magnesium are added by impregnation.
 6. The catalyst of claims 1, 3 or 5 wherein the zeolite is ZSM-5.
 7. The catalyst of claims 1, 3 or 5 wherein the zeolite is ZSM-11.
 8. The catalyst of claims 1, 3 or 5 wherein the zeolite is ZSM-12.
 9. The catalyst of claims 1, 3 or 5 wherein the zeolite is ZSM-35.
 10. The catalyst of claims 1, 3 or 5 wherein the zeolite is ZSM-38.
 11. A method for making a crystalline aluminosilicate zeolite catalyst having a crystal size of at least about 1 micron, a silica-to-alumina ratio of at least about 12 and a constraint index of about 1 to about 12, the step of incorporating into said zeolite catalyst a member comprising a Group 2B component, a Group 8 component and magnesium, said member having been incorporated in the order stated.
 12. The method of claim 11 wherein the zeolite is ZSM-5.
 13. The method of claim 11 wherein the zeolite is ZSM-11.
 14. The method of claim 11 wherein the zeolite is ZSM-12.
 15. The method of claim 11 wherein the zeolite is ZSM-35.
 16. The method of claim 11 wherein the zeolite is ZSM-38. 